The invention relates to mechanisms for pushbutton tuning of radio receivers and more particularly to improved keyslides and guides thereto.
Automatic pushbutton tuning of radio receivers using keyslide mechanisms are well known in the art. A detailed description of the operation of such mechanisms is given in U.S Pat. No. 3,195,359 to Alfred J. Clark. Briefly, a pushbutton radio is provided with a plurality of pushbuttons, each of which when depressed corresponds to a desired tuning of the radio receiver. The pushbutton connects to a button slide which is provided with a key slot. slideably fitted into the key slot is a T lug which extends from a tuner slide. The tuner slide couples to a memory cam which has opposing engaging faces.
To program a desired pushbutton tuning, the pushbutton is pulled outwardly from the radio receiver which releases the frictional forces maintaining the angular position of the cam. The receiver is then tuned manually to the desired frequency which rotates a treadle bar assembly having parallel rods constrained to move about an axis, which assembly couples to a movable carriage. The carriage relocates slugs within tuned coils which constitute the variable tuning element of the receiver. When the button is then depressed the opposing faces of the cam engage and align with the angular position of the treadle rods. Further pushbutton depression frictionally locks the angular position of the memory cam in the preselected position. Subsequent depression of the pushbutton will cause the face of the key slot to forcibly engage the T lug on the tuner slide thus forcing the slide and the cam against the treadle rods and aligning the rods to the angular position of the cam, thereby returning the radio receiver to the desired frequency.
As receiver tuning is dependent upon the angle to which the memory cam rotates the treadle bar assembly, maintaining angular position of the cam becomes quite critical. Errors in tuning can come about as a result of undesired movements of the cam. For example, in conventional pushbutton key-slide mechanisms, should the pushbutton be vertically deflected when it is depressed, the cam will be similarly deflected, causing an improper angular rotation of the treadle bar assembly and resultant receiver mistuning. As receivers are becoming miniaturized, the problems with undesired movements due to component tolerances becomes heightened.